This invention relates to a sheet metal nut and more particularly to a nut device which incorporates a compressible spring feature.
A growing trend in material selection, particularly in the automotive industry, is the supplanting of steel with a plastic-type material. Weight reduction, without an accompanying structural deficiency, is thus possible through the use of certain thermoplastic and/or composite thermoplastic materials. One of the inherent disadvantages of the use of a plastic material as a structural member or in a fastening joint is the tendency of plastic to cold flow or creep in response to a static force applied over a certain time period to a discrete region of the plastic surface.
Obviously, if a plastic material is used as a structural member under a very sensitive clamping load, as for example, in an application where the wheel rims of automobiles are formed of plastic, the cold flow problem becomes critical and must be overcome.
Accordingly, it is an object of this invention to provide a sheet metal nut which can reliably be utilized to clampingly engage a plastic workpiece.
A further more specific object of the invention is to provide a sheet metal nut which may be utilized as in the clamping securement of a plastic wheel in the hub of an automobile.
A particular advantage of the invention is the ability of a thin sheet metal device to distribute a clamping load over a wide surface area of plastic and in addition incorporate a spring feature which resiliently accommodates any force applied to the plastic material.
The above and other objects and advantages of the invention are obtained by a one-piece sheet metal nut basically including a tubular inner body region with internally formed threads and a substantially tubular outer body region connected at the uppermost extremities by a top wall. The lowermost region of the outer body is a frustoconical surface and the aperture created by the lower edge of the frustoconical surface is preferably greater than the inner diameter of the threaded bore. Spring means are formed in the upper portion of the nut and, in a preferred embodiment, the spring means is incorporated in the top wall. The inner body may axially move downwardly relative to the outer body to provide a resilient clamping load while permitting the frusto conical surface to remain in broad surface contact with the thermoplastic. Both the broad surface contact and the spring serve to overcome any inherent cold flow problems in the clamp joint.